trapped in a child's body

I'm looking for manga where a main character is stuck as a child. Where they've aged mentally but never grow up. I'm interested in the concept of them dealing with those around them aging and them not being able to.

I'm Not looking for manga where the main character looks like a kid but is an adult.

The best examples I can think of are stories involving vampires, like dance in the vampire bund or the girl from the movie Interview with a vampire.

I second Blood Alone.Chrno Crusade this should fit ok.Ookami to Koushinryou I think Horo could be counted in, unless you think 15 years old is too much. She's also very wise.Ubel Blatt but honestly I don't remember/know how really old is, so maybe I'm wrong.

________________What I like in Trivial Pursuit style. Pick your category:

I think the one you're looking for is Asatte no Houkou. It's about a child trapped in an adult body and a very realist adult trapped in a child's body (no they didn't swap body, they just aged up/down)